The present invention relates to the field of semiconductor integrated circuits. The invention is illustrated in an example with regard to a semiconductor integrated circuit cleaning technique, including a method and apparatus, but it will be recognized that the invention has a wider range of applicability. Merely by way of example, the invention can also be applied to the manufacture of raw wafers, lead frames, medical devices, disks and heads, flat panel displays, microelectronic masks, and other applications requiring high purity wet processing such as steps of rinsing, cleaning, drying, and the like.
Industry utilizes or has proposed various techniques to rinse and dry a semiconductor wafer. An example of a conventional technique used to rinse a wafer is a cascade rinse. The cascade rinse utilizes a cascade rinser which includes inner and outer chambers, each separated by a partition. Rinse water flows from a water source into the inner chamber. The rinse water from the inner chamber cascades into the outer chamber. An in-process wafer such as an etched wafer is typically rinsed in the cascade rinser by dipping the etched wafer into the rinse water of the inner chamber. This process is often used to neutralize and remove acid from the etched wafer.
A limitation with the cascade rinser is that xe2x80x9cdirty waterxe2x80x9d often exists in the first chamber. The dirty water typically includes residual acid as well as xe2x80x9cparticlesxe2x80x9d which often attach to the wafer. These particles often cause defects in the integrated often attach to the wafer. These particles often cause defects in the integrated circuit, thereby reducing the number of good dies on a typical wafer. Another limitation with the cascade rinser is wafers from the cascade rinser must still undergo a drying operation. A subsequent drying operation often introduces more particles onto the integrated circuit. More particles on the integrated circuit typically further decrease the number of good dies on the wafer. Accordingly, the cascade rinse often cannot clean or remove particles from the wafer.
Another technique often used to rinse wafers is the xe2x80x9cquick dumpxe2x80x9d method. The quick dump method relies upon the rapid deployment of water from the rinse tank to remove water and impurities from the semiconductor wafer. A limitation with this method is its inability to actually clean or remove particles from the wafer. In fact, the rapid deployment of water from the tank often transfers more particles onto the wafer. In addition, the wafers from the quick dump tank must still undergo a drying operation, further increasing the number of particles on the wafer. As previously noted, more particles often relates to lower die yields on the semiconductor wafer.
A further technique used to both rinse and dry wafers relies upon a spin rinse/dryer. The spin rinse/dryer uses a combination of rinse water spray to rinse and centrifugal force to remove water from the semiconductor wafer. The dry step often removes the water from the semiconductor wafer substantially by centrifugal force and evaporation. However, the spin rinse/dryer often introduces more particles onto the wafer. In fact, initially dissolved or suspended contaminants such as particles in the water are often left on the semiconductor wafer, thereby reducing the number of good dies on the wafer. Another limitation with the spin rinse/dryer is its complex mechanical design with moving parts and the like. The complex mechanical design often leads to certain problems such as greater downtime, wafer breakage, more spare parts, greater costs, among others. A further limitation is static electricity often builds up on the wafers during the spin cycle, thereby attracting even more particles onto the surface of the semiconductor. Accordingly, the spin rinse/drying does not clean or remove particles from the wafer.
Other techniques used to dry wafers include an isopropyl alcohol (IPA) vapor dryer, full displacement IPA dryer, and others. These IPA-type dryers often rely upon a large quantity of a solvent such as isopropyl alcohol and other volatile organic liquids to facilitate drying of the semiconductor wafer. An example of such a technique is described in U.S. Pat. No. 4,911,761, and its related applications, in the name of McConnell et al. and assigned to CFM Technologies, Inc. McConnell et al. generally describes the use of a superheated or saturated drying vapor as a drying fluid. This superheated or saturated drying vapor often requires the use of large quantities of a hot volatile organic material. The superheated or saturated drying vapor forms a thick organic vapor layer overlying the rinse water to displace (e.g., plug flow) such rinse water with the drying vapor. The thick organic vapor layer forms an azeotropic mixture with water, which will condense on wafer surfaces, and will then evaporate to dry the wafer.
A limitation with this type of dryer is its use of the large solvent quantity, which is hot, highly flammable, and extremely hazardous to health and the environment. Another limitation with such a dryer is its cost, which is often quite expensive. In fact, this dryer needs a vaporizer and condenser to handle the large quantities of hot volatile organic material. Still further, it has been determined that large quantities of hot volatile organic material are typically incompatible with most photoresist patterned wafers, and are also detrimental to certain device structures.
Still another technique relies upon a hot deionized (DI) process water to rinse and promote drying of the semiconductor wafer. By way of the hot DI water, the liquid on the wafer evaporates faster and more efficiently than standard room temperature DI water. However, hot water often produces stains on the wafer, and also promotes build-up of bacterial and other particles. Hot water can also damage the semiconductor, thereby reducing the amount of good dies on the wafer. Another limitation is water is often expensive to heat, and hot DI water is also an aggressive solvent. As an aggressive solvent, it often deteriorates equipment and facilities, thereby increasing maintenance operation costs.
As line size becomes smaller and the complexity of semiconductor integrated circuits increases, it is clearly desirable to have a cleaning technique, including a method and apparatus, that actually removes particles, prevents additional particles, and does not introduce stains on the wafers. The cleaning technique should also dry the wafers, without other adverse results. A further desirable characteristic includes reducing or possibly eliminating the residual water left on wafer surfaces and edges when water is removed (a meniscus). The water left on such surfaces and edges often attracts and introduces more particles onto the semiconductor wafer. The aforementioned conventional techniques fail to provide such desired features, thereby reducing the die yield on the semiconductor during wet processes.
From the above, it is seen that a cleaning method and apparatus for semiconductor integrated circuits that is safe, easy, and reliable is often desired.
The present invention provides a safe, efficient, and economical method and apparatus to clean an article (or object) such as a semiconductor wafer. In particular, the present method provides an improved technique that actually removes or reduces the amount of particles from the semiconductor substrate and also effectively cleans the substrate. The present method also provides an in situ cleaning system with substantially no mechanical movement of the substrate.
One aspect of the present invention provides a method for cleaning a semiconductor wafer. The present method includes immersing a wafer in a liquid comprising water. The wafer has a front face, a back face, and an edge. The method also includes providing a substantially particle free environment (e.g., ultra-clean gas, ultra-clean non-reactive gas, etc.) adjacent to the front face and the back face as the liquid is being removed. A step of introducing a carrier gas comprising a cleaning enhancement substance (e.g., trace amount of polar organic compound, helium, surfactants, carbon dioxide, etc.) during the providing step also is included. The cleaning enhancement substance dopes the liquid which is attached to the front face and the back face to cause a concentration gradient of the cleaning enhancement substance in the attached liquid to accelerate fluid flow of the attached liquid off of the wafer.
Another aspect of the invention provides an apparatus for cleaning a semiconductor wafer. The present apparatus includes a vessel adapted to immerse a wafer in a liquid comprising water. This wafer includes a front face, a back face, and an edge. The apparatus also includes a first control valve operably coupled to the vessel, and adapted to provide a substantially particle free environment adjacent to the front face and the back face as the liquid is being removed. A second control valve operably coupled to the vessel also is provided. The second control valve is adapted to introduce a carrier gas comprising a cleaning enhancement substance. The cleaning enhancement substance dopes the liquid which is attached to the front face and the back face to cause a concentration gradient of the cleaning enhancement substance in the attached liquid to accelerate fluid flow of the attached liquid off of the wafer.
A further alternative embodiment provides an apparatus for holding a plurality of substrates. The apparatus includes a lower support. The lower support comprises a plurality of first ridges, where each of the first ridges provides a support for a lower substrate portion. The apparatus also includes an upper support. The upper support comprises a plurality of second ridges, were each of the second ridges provides a support for an upper substrate portion. The lower substrate portion and the upper substrate portion are defined on a substrate. The first ridges and the second ridges draw liquid from the substrate.
A further understanding of the nature and advantages of the present invention may be realized by reference to the latter portions of the specification and attached drawings.